1. Field of the Invention
The invention pertains generally to the recording of graphical displays for three dimensional objects and is more particularly directed to providing a technique for generating graphical representations without displaying hidden lines.
2. Prior Art
In scientific and engineering endeavors there is a continuing need for the accurate replication of micro-surfaces by graphical displays. Enlarging the discontinuities and irregularities of these by graphical means allows personnel to study the characteristics and physical behavior of the materials forming the surfaces. Particularly, those investigating the surfaces of complex large scale integrated circuits and the surfaces of paper products have found this technique useful.
The science of micro-topography has until recently been at a disadvantage in not having an accurate and advantageous device for recording such representations. However, there has been developed an advantageous device capable of converting the three-dimensional motion of a micro-stylus into an enlarged two-dimensional graphical recording which appears to be three-dimensional.
This device uses a vertically sensitive micro-stylus transducer and an amplifier for scanning a specimen, coupled to a highly accurate X-Y recorder device. A precision reference carriage guides the micro-stylus linearly across the reference specimen to be studied in a series of closely spaced X-axis direction parallel tracks, and a precision carriage may be used to continuously or incrementally move the specimen slowly in the Y-axis direction during each trace. The X-Y recorder records the amplified traces of the micro-stylus across the reference specimen and the Z-axis motion of the micro-stylus is converted into an additional X- or Y-axis motion of the recording device to draw an apparent three-dimensional picture of the surface of the specimen. Alternatively, the specimen may remain fixed and the stylus partake of both the X-axis motion and the Y-axis motion; also the stylus may remain fixed and the specimen partake of both the X- and Y-axis motions.
A micro-topography device of this general description is more fully described in U.S. Pat. No. 3,675,333 issued July 11, 1972 to Gardner P. Wilson and assigned to Gould, Inc., the assignee of the present invention. The disclosure of the Wilson patent is hereby expressly incorporated by reference in the present description.
Many of the details of surfaces that are of interest to the micro-topographer may be difficult to describe or visualize in the two-dimensional topographical representations because of the "overwriting" of previously recorded scan lines. This phenomenon is caused by a subsequent scan line having an excursion on the ordinate axis which causes it to intersect a previously written scan line, thereby writing through or "overwriting" the previously written scan line. To provide a clear and acceptable graphic record of a relief configuration or specimen, it is therefore necessary to suppress these overwriting excursions as hidden or unseen lines.
In computer graphics the hidden line problem has been solved in the past by memorizing where each line has been written and not overwriting those lines already recorded. Normally this necessitates a block of memory and a special algorithm or the like to indicate where to start and stop the stylus of a recording device. This indirect control process is an expensive and time-consuming way of providing hidden line suppression capability. It would therefore be advantageous to provide a direct control writing technique to produce two-dimensional topographical representations of three-dimensional surfaces with hidden contours.